I wish I knew him
I wish i know him– ‘Wish’ must use the subjunctive, so the 2nd is wrong; it is indicative mood.
It was imperative that he found a job.
It was imperative that he find a job.-- The 'it is imperative/important/etc form does not know require the subjunctive, so both are fine, as is ‘It is imperative that the finds her’.
The president requests that they stop it quickly.
The president requested that they stop it quickly.-- This seems to be the only pair that illustrates your point about present/past. Yes, both are fine.